Suppose the edge of the unit cell = a pm
Number of atoms present per unit cell = Z
Atomic mass of the element = M
∴‌‌ Volume of the unit cell =(a ‌pm)3
= (a×10−10 cm )3
=a3×10−30cm3
Density of the unit cell =

Mass‌of‌the‌unit‌cell

Volume‌of‌the‌unit‌cell

Mass of the unit cell
‌‌‌‌= Number of atoms in the unit cell × Mass of each atom = Z×m
where m= mass of each atom
m=

Atomic‌mass

‌Avogadro′s‌number

=

M

N0

∴‌‌ Density of the unit cell, ρ=

Z×M

a3 ×N0×10−30

g / cm3
where edge, a is in pm and molar mass, M in g mol‌–1.
Atomic mass can be calculated by using the expression
M=

ρ×a3×N0×10−30

Z

g mol−1